Active studies have been made to ionic conductors, particularly oxygen ion conductors, which are electrolytes used in electrochemical devices, such as gas sensors and fuel cells.
Currently, in solid oxide fuel cell (“SOFC”) applications, it has been known that yttrium stabilized zirconia (“YSZ”) is the most suitable material for use as a high-temperature SOFC electrolyte. However, a doped ceria-type is more suitable for a low-temperature (lower than 600° C.) SOFC. In a high-temperature SOFC using any other electrolyte (doped ceria or La0.8Sr0.2GaO3-δ) than YSZ, materials such as La0.9Sr0.1AlO3-δ or Gd2Zr2O7 can be used as a protective layer of a cathode. An ionic conductor membrane for use in an oxygen pump should have both electrical conductivity and ionic conductivity. Accordingly, doped ceria, rather than YSZ with very low electrical conductivity, is suitable to be used in an oxygen pump.
Although all the materials as described above have a certain potential in industrial applications, they have merits and demerits depending on particular application to which they are applied. It is thought that this is because each material shows different ion conductivity characteristics and physicochemical properties depending on temperatures due to its unique feature such as crystalline structure or ion defect structure. Therefore, it is very important to develop new materials having various ion conductivity characteristics required for various applications. Such materials may result in the rapid development of relevant technologies requiring ion conductors.